PERST# is active low according to the PCIe specification.
However, the existing pcie-dw-rockchip.c driver does:
gpiod_set_value(..., 0); msleep(100); gpiod_set_value(..., 1);
When asserting + deasserting PERST#.
This is of course wrong, but because all the device trees for this
compatible string have also incorrectly marked this GPIO as ACTIVE_HIGH:
$ git grep -B 10 reset-gpios arch/arm64/boot/dts/rockchip/rk3568*
$ git grep -B 10 reset-gpios arch/arm64/boot/dts/rockchip/rk3588*
The actual toggling of PERST# is correct.
(And we cannot change it anyway, since that would break device tree
compatibility.)
However, this driver does request the GPIO to be initialized as
GPIOD_OUT_HIGH, which does cause a silly sequence where PERST# gets
toggled back and forth for no good reason.
Fix this by requesting the GPIO to be initialized as GPIOD_OUT_LOW
(which for this driver means PERST# asserted).
This will avoid an unnecessary signal change where PERST# gets deasserted
(by devm_gpiod_get_optional()) and then gets asserted
(by rockchip_pcie_start_link()) just a few instructions later.
Before patch, debug prints on EP side, when booting RC:
[ 845.606810] pci: PERST# asserted by host!
[ 852.483985] pci: PERST# de-asserted by host!
[ 852.503041] pci: PERST# asserted by host!
[ 852.610318] pci: PERST# de-asserted by host!
After patch, debug prints on EP side, when booting RC:
[ 125.107921] pci: PERST# asserted by host!
[ 132.111429] pci: PERST# de-asserted by host!
This extra, very short, PERST# assertion + deassertion has been reported
to cause issues with certain WLAN controllers, e.g. RTL8822CE.
Fixes: 0e898eb8df4e ("PCI: rockchip-dwc: Add Rockchip RK356X host controller driver")
Tested-by: Jianfeng Liu <liujianfeng1994(a)gmail.com>
Tested-by: Heiko Stuebner <heiko(a)sntech.de>
Signed-off-by: Niklas Cassel <cassel(a)kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam(a)linaro.org>
Cc: stable(a)vger.kernel.org # 5.15+
---
Changes since v2:
-Picked up tag from Heiko.
-Change subject (Bjorn).
-s/PERST/PERST#/ (Bjorn).
drivers/pci/controller/dwc/pcie-dw-rockchip.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/pci/controller/dwc/pcie-dw-rockchip.c b/drivers/pci/controller/dwc/pcie-dw-rockchip.c
index d6842141d384..a909e42b4273 100644
--- a/drivers/pci/controller/dwc/pcie-dw-rockchip.c
+++ b/drivers/pci/controller/dwc/pcie-dw-rockchip.c
@@ -240,7 +240,7 @@ static int rockchip_pcie_resource_get(struct platform_device *pdev,
return PTR_ERR(rockchip->apb_base);
rockchip->rst_gpio = devm_gpiod_get_optional(&pdev->dev, "reset",
- GPIOD_OUT_HIGH);
+ GPIOD_OUT_LOW);
if (IS_ERR(rockchip->rst_gpio))
return PTR_ERR(rockchip->rst_gpio);
--
2.44.0
Rockchip platforms use 'GPIO_ACTIVE_HIGH' flag in the devicetree definition
for ep_gpio. This means, whatever the logical value set by the driver for
the ep_gpio, physical line will output the same logic level.
For instance,
gpiod_set_value_cansleep(rockchip->ep_gpio, 0); --> Level low
gpiod_set_value_cansleep(rockchip->ep_gpio, 1); --> Level high
But while requesting the ep_gpio, GPIOD_OUT_HIGH flag is currently used.
Now, this also causes the physical line to output 'high' creating trouble
for endpoint devices during host reboot.
When host reboot happens, the ep_gpio will initially output 'low' due to
the GPIO getting reset to its POR value. Then during host controller probe,
it will output 'high' due to GPIOD_OUT_HIGH flag. Then during
rockchip_pcie_host_init_port(), it will first output 'low' and then 'high'
indicating the completion of controller initialization.
On the endpoint side, each output 'low' of ep_gpio is accounted for PERST#
assert and 'high' for PERST# deassert. With the above mentioned flow during
host reboot, endpoint will witness below state changes for PERST#:
(1) PERST# assert - GPIO POR state
(2) PERST# deassert - GPIOD_OUT_HIGH while requesting GPIO
(3) PERST# assert - rockchip_pcie_host_init_port()
(4) PERST# deassert - rockchip_pcie_host_init_port()
Now the time interval between (2) and (3) is very short as both happen
during the driver probe(), and this results in a race in the endpoint.
Because, before completing the PERST# deassertion in (2), endpoint got
another PERST# assert in (3).
A proper way to fix this issue is to change the GPIOD_OUT_HIGH flag in (2)
to GPIOD_OUT_LOW. Because the usual convention is to request the GPIO with
a state corresponding to its 'initial/default' value and let the driver
change the state of the GPIO when required.
As per that, the ep_gpio should be requested with GPIOD_OUT_LOW as it
corresponds to the POR value of '0' (PERST# assert in the endpoint). Then
the driver can change the state of the ep_gpio later in
rockchip_pcie_host_init_port() as per the initialization sequence.
This fixes the firmware crash issue in Qcom based modems connected to
Rockpro64 based board.
Cc: <stable(a)vger.kernel.org> # 4.9
Reported-by: Slark Xiao <slark_xiao(a)163.com>
Closes: https://lore.kernel.org/mhi/20240402045647.GG2933@thinkpad/
Fixes: e77f847df54c ("PCI: rockchip: Add Rockchip PCIe controller support")
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam(a)linaro.org>
---
drivers/pci/controller/pcie-rockchip.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/pci/controller/pcie-rockchip.c b/drivers/pci/controller/pcie-rockchip.c
index 0ef2e622d36e..c07d7129f1c7 100644
--- a/drivers/pci/controller/pcie-rockchip.c
+++ b/drivers/pci/controller/pcie-rockchip.c
@@ -121,7 +121,7 @@ int rockchip_pcie_parse_dt(struct rockchip_pcie *rockchip)
if (rockchip->is_rc) {
rockchip->ep_gpio = devm_gpiod_get_optional(dev, "ep",
- GPIOD_OUT_HIGH);
+ GPIOD_OUT_LOW);
if (IS_ERR(rockchip->ep_gpio))
return dev_err_probe(dev, PTR_ERR(rockchip->ep_gpio),
"failed to get ep GPIO\n");
---
base-commit: 4cece764965020c22cff7665b18a012006359095
change-id: 20240416-pci-rockchip-perst-fix-88c922621d9a
Best regards,
--
Manivannan Sadhasivam <manivannan.sadhasivam(a)linaro.org>